1. Field of the Invention
The invention relates to a spread spectrum receiving apparatus for receiving a spread spectrum signal.
2. Related Background Art
Hitherto, in a spread spectrum communication using a convolver, as shown in FIG. 10, a communication partner is determined by collations of diffusion codes CODE.sub.1 to CODE.sub.n which terminals T.sub.1 to T.sub.n and T.sub.1 ' to T.sub.n ' have as shown in FIG. 10.
Namely, an apparatus cannot communicate with a terminal equipment having another code and can communicate with a terminal equipment of only the same code.
FIG. 11 is a block diagram briefly showing the above principle.
In FIG. 11, a reception wave inputted from an antenna (not shown) is down converted into a desired IF frequency and is supplied to one input terminal 2a of a correlator 1.
A reference signal which has previously been diffused by, for example, the diffusion code CODE.sub.1 is inputted from a reference signal generation unit 4 to another input terminal 2b of the correlator 1. Only in the case where the diffusion code which the received signal from the input terminal 2a has is equal to CODE.sub.1, namely, when it is the same code as the diffusion code which the reference signal has, a correlation peak as shown in the diagram is outputted from an output terminal 3 of the correlator 1. The transmission data can be demodulated on the reception side by using such a correlation peak.
Even when the received signal using a code different from the code CODE.sub.1 which the reference signal has is inputted to the input terminal 2a, no correlation peak is outputted and the data cannot be demodulated.
In the above conventional example, however, there is a problem such that when the frequency of the reference signal is deviated from the frequency of the received signal, the value of the correlation peak decreases.
In addition, the number of diffusion codes cannot be set to an infinite value and the diffusion codes need to be mutually orthogonal with each other as much as possible. Therefore, the number of codes which can be used is limited and the number of terminals which can be used in the same band is also limited.